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MAN-147-0018-A
5.3.
P
RESSURE
S
ENSOR
I
NPUTS
5.3.1.
R
E
-
ZERO
F
ACILITY
(
FOR PRESSURE RELATIVE TO LOCAL ATMOSPHERE
)
Pressure sensors supplied by HWM normally measure pressure relative to atmospheric
pressure. Since there can be some variation in local atmosperic pressure (e.g., due to
altitude), the loggers have a facility to re-zero the pressure sensor.
This must be done
with the sensor exposed to atmospheric air
.
Prior to
connecting the transducer to the actual measuring point, leave it exposed to
air
. Then “re
-
zero” the sensor using the
method found in the IDT user-guide.
5.3.2.
P
RESSURE
S
ENSOR
(I
NTERNAL
)
A pressure input may be presented as a built-in transducer (as shown in Figure 9, on
page 12), which connects directly to the fluid via a hose using a quick-release connector.
Note:
Do not connect the sensor to the measurement point before going through the
re-zero
(to local atmospheric pressure) process, if required.
Connect the pressure tapping on the pipe (measurement point) to the pressure
transducer of the logger using a suitable interconnecting hose. (For an example, see
Figure 11.) Ensure the hose is bled, for correct operation.
This interface is factory calibrated. No on-site calibration is required.
Note: Add insulation to the pipe
and logger to prevent
freezing.
If the water in the hose or
the logger itself freezes,
there is a danger of
permanent damage to the
pressure transducer.
5.3.3.
P
RESSURE
S
ENSOR
(E
XTERNAL
)
A pressure input may be presented as an electrical interface, using a 4-pin or 6-pin
MIL-Spec connector (see Figure 8 on page 12).
Cabled pressure sensors for the Multilog2 are available from HWM. For most situations,
sealed type pressure (or depth) sensors are used, and the sensor will be
wired directly to the connector, as shown in Figure 12.
Pressure point
on pipe
Pressure input
(For illustration purposes only.
Logger shown is not Multilog2.)
Figure 11. Example connection to a built-in pressure transducer
